Pressure sensitive hot melt adhesive for sanitary products

Patent and Patent Specification of PERSONAL PRODUCTS COMPANY, USA, (state: New Jersey), industrial and commercial, domiciled in Van Liew Avenue, Millton, New Jersey 08850, United States, for PREPARATION OF A HOT FUSIBLE PRESSURE SENSITIVE STICKER FOR HYGIENIC PRODUCTS.

Descriptive Memory

Background of the invention

The present invention relates to pressure sensitive adhesive compositions and in particular to compositions which are applied to a hot or molten substrate and which form upon cooling a relatively gummy and pressure sensitive adhesive. In this way, the substrate may adhere to another surface by applying pressure and may subsequently be removed by peeling it off this surface.

In a specific embodiment, the present invention relates to pressure sensitive hot melt adhesives applied to the surface of articles which serve to absorb and retain body fluids such as diapers, sanitary napkins and bandages. In the case of sanitary napkins, for example, the dressing has a body-facing face and a underwear-facing face. The pressure-sensitive adhesive is applied to the clothing-facing face and attaches the dressing to the back portion. lingerie legs,

CR.

<img file="PT77243B_D0001.tif" />

keeping the dressing fixed during use. Of course, in such cases it is convenient for the dressing to adhere tenaciously to the underwear after it has been pressurized so that the dressing does not move or come off due to the pressure exerted on the adhesive bond due to normal body movements of the dressing. wearer. On the other hand, it is important that the dressing completely peels off the underwear after use without leaving any residue on the garment.

Pressure sensitive adhesive formulations abound in the art today for use in body exudate absorbent products such as sanitary towels. In general, these existing proposals can be classified into two groups, namely water-based adhesive systems and so-called hot melt systems. In the use of these prior systems, several drawbacks have been encountered in attempts to meet the above criteria of firm attachment and clean take-off.

Specifically, water-based systems suffer from the problem of drying or slow placement. Basically, these water based systems require the initiation of a high water content in order to have sufficient liquid flow characteristics to be applied to a substrate, with the high production speed required for the economical manufacture of disposable products such as water. like the sanitary towels and diapers. Unfortunately, this high water content necessitates a long drying or corresponding laying time, which in turn slows down the production process.

In an attempt to solve this problem, the technique has turned to so-called pressure sensitive hot-melt systems, the main ingredients of which are thermoplastic elastic polymers in combination with plasticizers, gummings, additives, pigments, antioxidants and other stabilizers. These hot melt adhesive formulations are exemplified by US Pat.⁹ No. 4,136,699 issued January 30, 1979 to JA Collins et al .; US Patent No.⁹ 3,554,940 issued January 12, 1971 to M.Arakawa et al .; US Patent No.⁹ 3,917,607 issued to RK Crossland et al.

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November 1975; US Patent No.⁹3 239,478 issued to Harlan, Jr. in March 1966; US Patent No.⁹ No. 3,686,107 issued August 22, 1972 to T. Russell; US Patent No.⁹ No. 3,862,068 issued January 21, 1975 to T. Russell; US Patent No.⁹ 3,954,692 issued May 4, 1976 to REDownery; US Patent No.⁹ No. 3,935,338 issued January 27, 1976 to WJRobinson et al .; US Patent No.⁹ 3,932,327 issued January 13, 1976 to F. Naylor; US Patent No.⁹ No. 3,956,223 issued May 11, 1976 to J. Chiang, and US Patent No.⁹4 028 292 issued June 7, 1977 to R. Korpman.

In each of these earlier proposals, the ingredient ratios, molecular weights and chemical nature of the various additives are selected to produce an adhesive composition which has sufficient flow properties when heated to be applied to a substrate and which can rapidly cool and form. a pressure sensitive adhesive which bonds this substrate to another with a satisfactory degree of toughness. Unfortunately, until now these earlier proposals have been at most a compromise between toughness and clean take-off, although they represent an improvement over water-sensitive adhesives. Generally, in order to obtain a clean peel off of the underwear, such as adhesive-fixed sanitary towels, tenacity has been sacrificed.

Summary of the invention

It has now been found that a hot melt pressure sensitive adhesive can be obtained which is tailor made to address the shortcomings of the prior art compositions. It is specifically selected to have certain rheological properties that manifest themselves in the desired yield criteria, namely tenacious bonding and clean take off.

Specifically, it has been found that an adhesive formulation can be selected on the basis of an easily obtainable stress-strain analysis by identifying the rheological properties that apply in particular to the dynamics of bonding a pressure sensitive hot melt adhesive to substrate and subsequently remove this

<img file="PT77243B_D0004.tif" />

hot fusible material from the substrate. It has now been taken into account that the bonding process is relatively slow, where the tension is applied for a relatively long period of time, and where, after this tension is applied, elastic recovery can also take place over a long period. of time. On the other hand, in the take-off operation, the tension is applied quickly and the elastic recovery has to be done in a short time. In other words it is important that visco-elastic materials chosen for use in a hot melt composition have relatively viscous material behavior under pure dynamic stress when subjected to prolonged stress and long recovery period. At the same time, this viscoelastic material should be selected to have elastic properties when subjected to pure dynamic stresses imposed quickly and having only a short recovery period.

In accordance with the present invention, the selection of a suitable adhesive can be made by performing an analysis of the rheological properties of the composition by means of an easily obtainable instrument for characterizing viscoelastic materials - a thermomechanical spectrometer. Basically, this instrument is intended to impose on the test sample a selected strain that varies with the sample temperature in a known manner, i.e., sinusoidal curve. The stress function related to this strain is detected by the instrument and the stress-strain ratios are interpreted by integral microprocessing and graphically expressed as temperature dependent rheological functions such as the accumulation module, the loss module, and the ratio of the two modules known as tangè>. As a function of temperature, these parameters are in fact analogous to the same parameters as a function of time, which is based on the known rheological principle of time-temperature overlap. Thus, the parameters produced by the thermomechanical spectrometer describe the stress-strain properties of a given material under dynamic conditions.

It has been found that a hot melt adhesive having certain critical parameters by analysis in the thermomechanical spectrometer is unique in its suitability to meet the tenacious and low binding criteria.

<img file="PT77243B_D0005.tif" />

clean, and with respect to these criteria will represent a substantial improvement compared to the hot melt compositions currently known in the art. In particular, it has been found that the hot melt adhesive composition should be selected to have a transition temperature from the glass phase to the elastic phase which is in the range of 0 ° C.⁹C and 10⁹C. In addition, the composition must have a temperature difference between the transition temperature from the glass to the elastic phase and the flow temperature of 45 ° C.^?C and 55^?C. The accumulation module according to the transition temperature from the glass phase to the elastic phase and the flow temperature shall be a function of the monotonic decreasing temperature and shall have a value in the arithmetic mean between the transition temperature from the glass phase to the glass phase. the elastic phase and the temperature of

5th flow, between 3.5x10 and 6.5 x 10 dynes / cm2.

The slope of the log ^ Q function of the accumulation module (in dynes / cm2) with respect to temperature (in ⁹C) shall be from -0.005 to -0.025 at a temperature equal to the arithmetic mean of the glass-to-elastic phase transition temperature and the flow temperature.

It is to be understood that the above parameters are defined in terms of mechanical spectrometer test analysis performed under the conditions specified below.

The formulations should also have stable properties and not be subject to degradation, for example by oxidation, for a substantial period of time. Thus, the composition should not exhibit a substantial reduction in viscosity when maintained for 90 hours at 350 ° C.⁹F (176.7⁹C) in exposure to air.

Needless to say, the components chosen for a specific composition which fulfill the above rheological properties must be equally compatible to the extent that a homogeneous mixture can be prepared and maintained. In other words, the surface adhesive properties of a given adhesive composition mass should not vary significantly. relative to the rest of the mass.

* When the above parameters are met

<img file="PT77243B_D0006.tif" />

established, an adhesive capable of combining high toughness with clean take-off to a degree hitherto not exceeded by any known composition, and at the same time capable of being stored in a melt state for some time without unacceptable degradation.

Description of the drawings

The present invention will be better understood by examining the following description in conjunction with the accompanying drawing, which is a typical rheological analysis produced by a thermomechanical spectrometer, illustrating the accumulation modulus, the loss modulus and tangó as temperature functions.

Detailed Description of the Invention

As mentioned above, the present invention comprises selecting from a wide variety of available viscoelastic polymeric compositions one which is particularly suited to meet the requirements of tenacious bonding and clean peel and which, moreover, are not suitable for use. degrade with time.

The viscoelastic polymer of choice, the main ingredient in the formulation of this invention, is of the ABA block copolymer type and specifically the type where the middle block (i.e. part B) contains polyolefins such as ethylene and butylene copolymers. . The final block (part A) contains polystyrene.

Shell Oil Company supplies a wide variety of elastic copolymers and sells them under the brand name KRATON. ^{and in es}P^eci^Thel under ^The KRATON G. The KRATON G series of elastic polymers come in a wide range of average molecular weight values ​​and weight ratios between end blocks and middle blocks. For example, KRATON G may be obtained wherein the average molecular weight value of blocks A ranges from 7000 to about 30,000 and blocks A may constitute about 10-50% by weight of the block copolymer. Within these broad limits of available KRATON G-type polymers materials may be selected to produce a full spectrum of rheological properties in adhesives ranging from relatively elastic to relatively viscous flow properties under static conditions and at a given temperature.

<img file="PT77243B_D0007.tif" />

In selecting a suitable viscoelastic material, the user faces the problem of having to carry out a large number of empirical experiments before making a choice. This problem is greatly aggravated when the aim is to achieve adhesive behavior under varying dynamic conditions, as is the case, for example, when selecting a viscoelastic material suitable for use in sanitary napkins. In general the adhesive composition for this purpose is applied by the manufacturer in the melt state to the face of the sanitary napkin which will be against the underwear, and is covered with a peelable protective strip. The user, just prior to use, removes the detachable strap and places the dressing by pressing it against the inner surface of the crotch part of the underwear. 0 The adhesive, under the influence of the tension exerted on it as a result of the wearing of the dressing by the wearer, deforms and flows to the irregularities of the surface of the garment and attaches to it. Once the tension exerted by the wearer has ceased, the adhesive recovers and over time reaches a state of equilibrium deformation which for all practical purposes can be considered constant, although it should not be forgotten that most likely and recovery, although small, continue to take place. In order to maximize bond toughness, an extremely slow recovery is ideal, where steady state is achieved with a low recovery percentage.

When removing the dressing from the inner garment, the wearer generally takes one end of the dressing and quickly detaches it from the underwear, applying a quick strain on the adhesive. In such fast deforming conditions, an equally quick recovery of the dressing is ideal. deformation, i.e. that the adhesive layer has sufficient cohesive force to ensure a clean peel off of the garment.

The problem of the formulation of adhesives has been further complicated by the fact that while in determining a composition a height may exhibit an approximation of the ideal rheological properties described above, these properties may change over time as the polymers change. They degrade or oxidize when exposed to air. Thus there is no guarantee that consistent results can be maintained during use.

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It has now been found that the extremely difficult task of selecting a satisfactory composition from the wide variety of KRATON G adhesive compositions through empirical experiments has been greatly facilitated by the applicants' verification that the desired optimal behavior corresponds to certain critical rheological properties. , time dependent, of adhesive composition. In addition, these properties have made it possible to define an adhesive composition which by use far exceeds the results of any previously known composition obtained by experimentation.

The novel adhesive composition referred to in the present invention is characterized by certain time-dependent basic rheological properties which are determined by means of a thermomechanical spectrometer. This analysis is intended to describe the characteristics of a viscoelastic material and to take into account the phase switching between stress and strain. On the other hand, the application of the principle of time-temperature overlap the time variable proves to be analogous to a temperature variable that can be easily measured.

Assuming a certain degree of simplification, when a certain stress is applied to a viscoelastic material as a function of time, the corresponding strain tends to be delayed by the stress function. Similarly, if time-dependent deformation £ (t) is a time sinusoidal function such that:

£ (t) = sen (A t) where £_m If the amplitude, the time and the angular velocity in radians per unit of time, then the corresponding time-dependent voltage σ '(t) will also be sinusoidal but will be delayed by such an angle that:

&lt;/ (t) = sen (uJ t + S) that can develop into:

(t) cos

- <f & m m sin (GJ t) cos sin (x / t) + sin sin (o) t) + _m^{sen cos}t> mm (ιΛ / t)

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= G 'sen (ll) t) + G cos (d) t);

where G '= cos 6 and G = sençç; and wherein, for a given sample and at a given temperature, under sinusoidal stress at a constant angular velocity, G 'and G will be unique time functions. Parameter G 'is called accumulation modulus and G is called loss modulus. The ratio of G / G * is called tang á. Based on this, it can be concluded that the dynamic properties of an adhesive can be determined by determining the time dependent functions G ', G and tang. To get a complete definition of these functions by experimentation, an inconveniently long period of time is required, which makes a time-varying study impracticable. Fortunately, it has been found that these time-dependent functions have a direct analogy with temperature-related functions according to the well-known principle of time-temperature overlap (as described below).^or Rheology, Vol 2, directed by Frederick R. Eirich, 1858 Academic Press Inc., New York, on page 67). According to the simplest form of this principle, the curves of these functions and the log of these functions, represented as ordered with respect to log ^ Q Ho time represented as abeissa, can be overlapped with abeissa values ​​in log of temperature without changing the characteristics. of the curves. Thus, a long period of time equivalent to a high temperature and a short period of time is equivalent to a low temperature.

Thermomechanical spectrometer uses this principle of time-temperature overlap, replacing time data with temperature data. The sample to be tested is placed between two parallel plates and a deformation is caused which may be chosen to vary sinusoidally with the temperature. During the test the temperature is controlled by convection gas in a room chamber. The oscillation frequency can be chosen with the value^cons^OKarbitrary. The spectrometer is equipped with a transducer that actually senses the torque and normal force generated in response to the imposed strain. These forces are translated by means of a microcomputer integrated in the spectrum. meter, in tensions that in turn are translated by the logic of computer programs in the rheological functions of G ', G and tangd.

<img file="PT77243B_D0010.tif" />

The accompanying graph illustrates the rheological (analogous to time) temperature functions calculated from analysis with the thermomechanical spectrometer for an adhesive composition meeting the criteria established by the present invention. As this graph shows, the adhesive behaves quite differently at low temperatures (short time periods) compared to high temperatures (long time periods). Specifically, the material changes from a glassy state to an elastic state and a viscous flow state as the temperature rises from values ​​below T to values ​​above ^Tf

Some rheological properties can be set from these functions. Thus, the temperature at which the tang function reaches its maximum is called the glass transition temperature to the elastic phase of the composition, that is, the glass transition temperature of the middle block, T. The temperature at which function G reaches its second maximum is the flow temperature, Tf. Between T and Tf is a temperature zone which we call the elastic threshold zone.

It has been found that the desired criteria of tenacious bonding and clean take-off can be met at end use if an adhesive composition based on ABA KRATON G-type polymers is chosen because it has some of the rheological properties described above within strict limits, provided that the Choose a composition that maintains these properties for the expected shelf life.

Specifically, under the mechanical spectrometer parameters described herein, it has been found that the transition temperature from glassy to elastic phase must be within 0 ° C.⁹C and 10⁹C. The elastic plateau zone, the zone between the transition temperature from the glass phase to the elastic phase (T) and the flow temperature (Tf) shall be within the temperature range of 45 ° C.⁹C to 55⁹C. The accumulation module G 'should be a monotonic decreasing temperature function and should have a value of 3.5 x 10 6 to 6.5 x 10 6 dynes / cm 2 in most of the elastic threshold zone. More specifically, G 'should have

<img file="PT77243B_D0011.tif" />

““ '• Mm,., This value from 3.5 x 10 $ to 6.5 x 10 $ din.es/cm2 in the arithmetic mean of temperatures and that is, the temperature (T_y + Ί /) / 2, where T and Ί / are expressed in degrees centigrade. In addition, at this arithmetic mean temperature, the log ^ G 'function with respect to the temperature (where G' is expressed in dynes / cm2 and the temperature in⁹C) should have a slope d (log ^_Q G ') / d (T), from -0.005 to -0.025.

It is also important that the composition chosen be capable of maintaining the established rheological properties during the intended shelf life and during use. Thus, it has been found that the composition will satisfy this condition if selection is made on the basis of compositions that do not substantially reduce viscosity when kept in exposure to air for 90 hours at 350 ° C.⁹F (176.7⁹Ç). Not showing a substantial reduction in viscosity means that immediately after the 90 hour period the viscosity is not less than about 95% of the initial viscosity, and preferably not less than about 97% being the viscosity measured with a Brookfield viscometer.

Example 1

A first series of adhesive formulations of the following compositions are prepared:

Component ¾ by weight · Parts per 100 parts rubber

<td colspan="3">Sample 1</td>

<td>Kraton G 1652</td><td> 20,0</td><td> 100,0</td>

<td>Arkon P-85</td><td> 52,4</td><td> 262,0</td>

<td>Tufflo 6054</td><td> 25,6</td><td> 128,0</td>

<td>uncle₂</td><td> 1,0</td><td> 5,0</td>

<td>Ethyl 330</td><td> 1,0</td><td> 5,0</td>

<td>Sample 2</td><td></td><td></td>

<td>Kraton G 1657</td><td> 25,0</td><td> 100,0</td>

<td>Arkon P-85</td><td> 52,1</td><td> 208,0</td>

<td>Tufflo 6056</td><td> 20,9</td><td> 84,0</td>

<td>uncle₂</td><td> 1,0</td><td> 4,0</td>

<td>Ethyl 330</td><td> 1,0</td><td> 4,0</td>

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<td>Sample 3</td><td>&amp; «Ge ;;. ::; _. ._______ „</td><td></td>

<td>Kraton G 1652</td><td> 19,8</td><td> 100</td>

<td>5280 score</td><td> 59,5</td><td> 300</td>

<td>Shellflex 371</td><td> 19,8</td><td> 100</td>

<td>Butyl Zimate</td><td> 0,6</td><td> 3</td>

<td>Ethyl 330</td><td> 0,3</td><td> 2</td>

Kraton G series elastic polymers are ABA block copolymers with polystyrene end groups and a medium block of polyethylene and polybutylene copolymer, and with various molecular weights and various weight percentages in the end block polymer groups such as is defined below.

Arkon P-85 is used in these compositions as a gum resin and is a mixture of alicyclic compounds, aliphatic compounds and unsaturated unsaturated aromatic compounds with softening points at 85 ° C.⁹C. This resin is supplied by Arakawa Rinsan Kagaku Kogyo Company, Higashi-ku KK, Osakashi, Japan.

Tufflo 6054 and Tufflo 6056 are plasticizers, supplied by Atlantic Richfield Oil Company, and comprise mixtures of paraffinic, naphthenic and aromatic hydrocarbons with a weight percentage of aromatic hydrocarbons of about 13¾ and 5¾ respectively, based on gel-clay analysis.

Ethyl 330 is an antioxidant provided by Ethyl Corporation and comprises 1,3,5-trimethyl-2,4,6 tris ZZ 3,5-di-tert-butyl-4-hydroxybenzyl (benzene).

Score 5280 is a gumming resin provided by Exxon Corporation and comprises a mixture of alicyclic and short chain aliphatic hydrocarbons and a small amount of monosubstituted aromatic hydrocarbons. 0 softening point and about 85⁹

Ç.

Shellflex 371 is a plasticizer provided by Shell Oil Company and comprises a mixture of paraffinic, naphthenic and aromatic hydrocarbons. The aromatic weight percentage is about 34% by gel-clay analysis.

Butyl zimate is an antioxidant provided by RT Vanderbilt Company and comprises zinc Di-n-butyl dithiocarbamate.

<img file="PT77243B_D0012.tif" />

The above formulations are subjected to thermomechanical spectrometer analysis using a spectrometer manufactured by Rheometrics Inc. of Union, New Jersey. The geometric mode chosen for these tests is parallel plates and the oscillation frequency chosen is 1.0 radians per second. The results of the rheological analysis are presented in Table 1.

Sample stability is tested by measuring viscosity reduction with a Brookfield viscometer after the sample has been subjected to a temperature of 350 ° C.⁹F (176.7⁹C) for 90 hours. These results are shown in Table 1.

The adhesive formulations are tested to determine their results with respect to tenacious bonding properties and clean peel off.

A strip of the adhesive composition of the present invention is placed on a Sure and Natural Maxishield sanitary napkin manufactured by Personal Products Inc. of Milltown, New Jersey. The dressing comprises a generally rectangular absorbent body with a body facing face and a clothing facing face. A polyethylene film barrier sheet is glued to the side of the garment and secured with adhesive and a wrapping layer of fabric. 0 The whole is then wrapped in a generally rectangular covering of non-textile material. The edges of the non-textile material parallel to the longitudinal edges of the napkin overlap the face of the napkin facing the garment. A strip of the adhesive composition referred to in this example is placed.^mo^° ^The fi^car P^or above the overlapping edges of the cover. The strip has a length of six inches (15, 24 cm) and a width of 3/4 inch (1, § cm). The weight of the adhesive composition thus applied is 370 milligrams per dressing evenly distributed at a rate of 12.7 mg / cm 2.

To test the toughness of the adhesive bond, a Fast Fabric Peei Test is performed using the Peei and Release Tester of the Tag and Label Manufacturers Institute. Label Manufacturers Institute), manufactured by Testing Machines Incorporated of Amityville, New York. Prior to the test, the sanitary napkin is conditioned for 16 hours at a temperature

<img file="PT77243B_D0013.tif" />

from 21⁹C is a relative humidity of 65¾ along with a fabric made of 80 line per inch cotton in both machine direction and cross direction, and measuring 7 inches by 2 1/2 inches provided by Test Fabric

Inc. from Middlesex, New Jersey. After conditioning, the cotton wool is adhered to the dressing and both are compressed between two stainless steel plates at a maximum load of 150 pounds for one minute. The pressure is relieved and allowed to pass for 80 minutes to allow the system to equilibrate, after which the cotton fabric is peeled off the dressing using the stated test instrument at a take-off speed of 1200 inches per minute and a nominal take-off angle of 180^?. The value is expressed in grams of maximum force per inch of width across the take-off direction.

The rapid take-off is measured by successively carrying out five take-off tests as described above, except that the time between relieving pressure and the test is 1 minute instead of 80 minutes using the same cotton fabric in all cases. The tissue weight increase expressed in mg of adhesive per cm2 of adhesive area is determined.

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As Table 1 indicates, the elastic polymer showed significant variations in its chemical properties, such as molecular weight average value and molecular weight average value and the percentage weight of the elastic polymer in the polystyrene end groups. Also the weight percent of the elastic polymer showed significant variations in these formulations. However, the combination of these variables resulted in formulations that met the requirements of the present invention with respect to their rheological properties. In addition, each of the compositions is in accordance with the stability requirements set forth above.

Therefore, the results of using these adhesives are satisfactory. The stripping force_in equilibrium is in each case at least 700 g / inch, a value which has been found to ensure that a sanitary napkin, for example, remains fixed during use. This tenacious bond does not appear combined with a transfer of adhesive to the underwear fabric. These combined properties have not hitherto been exceeded with such stable adhesive formulations.

Comparison Example

In order to illustrate the advantages of the present invention a series of comparison samples was prepared with the following formulations:

Component% by weight Parts per 100 parts rubber

Sample 4

<td>Kraton G 1652</td><td> 15,0</td><td> 100</td>

<td>Arkon P-85</td><td> 55,8</td><td> 372</td>

<td>Tufflo 6054</td><td> 27,2</td><td> 181</td>

<td>uncle₂</td><td> 1,0</td><td> 7</td>

<td>Ethyl 330</td><td> 1,0</td><td> 7</td>

<td>Sample 5</td><td></td><td></td>

<td>Kraton G 1650</td><td> 14,9</td><td> 100</td>

<td>Arkon P-85</td><td> 53,5</td><td> 359</td>

<td>Tufflo 6054</td><td> 29,7</td><td> 199</td>

<td>uncle₂</td><td> 1,0</td><td> 7</td>

<td>Ethyl 330</td><td> 1,0</td><td> 7</td>

<img file="PT77243B_D0019.tif" />

Sample 6

Kraton G 1650

Wingtack 95 - Others

Sample 6 is a commercially available formulation whose composition is not fully known. Wingtack 95 is a gumming resin supplied by Goodyear Tire and Rubber Company and comprises a polymerized solid isopropene and piperylene gumifier with a softening point of about 95 ° C.⁹

Ç.

Samples are tested for redogical properties, stability, and results in use, analogous to Example 1. Results are shown in Table 2.

<img file="PT77243B_D0020.tif" />

<img file="PT77243B_D0021.tif" />

<img file="PT77243B_D0022.tif" />

As Table 2 indicates, the percent by weight of the elastic polymer, the percentage of polystyrene end groups, and the molecular weights of the polymer all fall within the range of values ​​for these parameters set out in Table 1. However, these parameters are combined in samples 4 to 6 to produce rheological properties outside the limits prescribed herein and, as Table 2 indicates, have substantially less satisfactory use results than the compositions of samples 1 to 6. 3 in accordance with the present invention.

Specifically, sample 4 has an accumulation module G 'below the prescribed limits of 3.5 x 10 6 to 6.5 x 10 6 dynes / cm2 at the mean temperature of the elastic plateau zone, ^TAvg. . As a result, while the equilibrium take-off value is close to satisfactory, the amount of residue is not acceptable.

Sample 5 has too large an interval between elastic plateau temperatures as well as a low G 'â T gj. In addition, the slope of the log function₁₀ G * relative to T â T_ffigj is too small. Practical results in use are insufficient balance take-off value.

Similarly, sample * 7 has a too large T and a small slope. Also here the result is an insufficient take-off value.

This sample also suffers from the disadvantage of insufficient stability as it has a viscosity reduction of 30¾ when kept for 90 hours at 35O⁹ F (176.7⁹Ç).

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